Once Again Through Time II

In the Old Phoenix, Taverner introduces:

"'Messer Leonardo da Vinci... Herr Doktor Albert Einstein....'"
-Poul Anderson, "House Rule" IN Anderson, Fantasy (New York, 1981), pp. 9-20 AT p. 17.

However, he later terminates their conversation:

"'No.'...
"'No, gentlemen,' he said in language after language...
"'I fear I must ask you to change the subject. You would learn more than should be. Both of you.'" (pp. 19-20)

But he does not stop the conversation between Prince Rupert and Valeria Matuchek even though, as a result of this conversation, Rupert returns to the Shakespearean timeline knowing that he must prevent a regicide and all its historical consequences.

Rupert has come from a timeline in which there is no regicide. Therefore, it is permissible, indeed probably necessary, that he return to that timeline and prevent regicide. Da Vinci has come from a timeline in which he did not later have any inkling of Einsteinian relativity. Therefore, it is necessary that he be prevented from conversing any further with Albert Einstein.

Taverner preserves existing timelines just as the Time Patrol preserves the Danellian timeline. We know what happens to the Danellian timeline if a time criminal succeeds despite the efforts of the Time Patrol whereas I am not sure what would happen to da Vinci's timeline if he did return to it with some knowledge of relativity.

It is also clear that da Vinci was possibly intelligent enough to suggest to Einstein where he was going astray, thus in turn changing the nature of Einstein's discoveries, as indeed happened in the goetic universe. See Speculative History.